Motor and motor drive system

ABSTRACT

Provided is a motor having a combination of a plurality of coil pairs and a permanent magnet, wherein these coil pairs are supplied with an excitation signal from a drive circuit so as to be excited at alternate opposite poles, and the permanent magnet is constituted such that the plurality of polar elements is disposed to become alternating opposite poles; the drive circuit is constituted to supply an excitation signal having a prescribed frequency to the coil pairs, and relatively move the coil pairs and permanent magnet with the magnetic attraction—repulsion between the coils and permanent magnet; and the drive circuit is constituted to supply to the coil pairs a waveform signal corresponding to the pattern of the back electromotive voltage to be generated in accordance with the relative movement between the coil pairs and permanent magnet.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a divisional patent application of U.S. Ser. No.11/070,406 filed Mar. 1, 2005, claiming priority to Japanese PatentApplication No. 2004-058064 filed Mar. 2, 2004, all of which areincorporated by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to various motors constituted to rotate arotor or move a slider formed from a permanent magnet or ferromagneticmaterial by linearly arranging coils that generate magnetic poles andsequentially switching the current to be applied to the coil, a magneticstructure to be employed in such a motor, and a power driver employingthis motor as its drive source. The present invention may be employed inthe likes of an electric vehicle, electric cart and electric wheelchair,as well as an electric toy, electric airplane, small electronicappliances and MEMS as the foregoing power driver.

2. Description of the Related Art

An AC motor driven with a frequency signal such as an alternatingcurrent can be broadly classified into two types; namely, a synchronousmotor and an induction motor. A synchronous motor is a motor that uses alayered core of a permanent magnet or a ferromagnetic material such asiron in the rotor, and rotates at a rotation speed that is the same asthe speed of the rotating magnetic field determined based on the powersupply frequency.

Depending on the type of rotor, there are various types of motors suchas a magnetic type which uses a permanent magnet, a coil type with acoil wound thereto, and a reactance type which uses a ferromagneticmaterial such as iron. Among the above, with the magnetic type motorrotates by the permanent magnet of the rotor being pulled with therotating magnetic field of the stator. Meanwhile, the induction motor isa motor that rotates by generating a separate magnetic field with theelectromagnetic induction effect to a rotor having a box-shapedconduction wire.

Among the foregoing motors, there is a motor that does not rotate, butrather moves linearly or moves freely on a flat surface. This kind ofmotor is generally referred to as a linear motor, and moves thepermanent magnet or ferromagnetic material mounted thereon by linearlyarranging coils that generate magnetic poles and sequentially switchingthe current to be applied to the coil. The linearly disposed coil arrayis the stator, and the rotor corresponds to a flat slider that slidesthereabove.

As a magnetic synchronous motor, for instance, there is a smallsynchronous motor described in the gazette of Japanese Patent Laid-OpenPublication No. H8-51745 (Patent Document 1). This small synchronousmotor, as shown in FIG. 1 of Patent Document 1, is constituted bycomprising a stator core 6 wound with an excitation coil 7, and a rotor3 having a rotor core 2 having a magnet 1 build therein and in which theNS poles are aligned in even intervals around the peripheral facethereof.

SUMMARY OF THE INVENTION

Nevertheless, when a rectangular wave is supplied to the coil of themotor explained in the foregoing conventional technology, the presentinventors newly discovered that the operation efficiency of the motordeteriorates significantly. Thus, an object of the present invention isto provide a motor superior in operation efficiency by controlling theexcitation signal to be supplied to the coil of the motor. Anotherobject of the present invention is to provide a motor superior in thegenerated torque characteristics. Still another object of the presentinvention is to provide a drive circuit of such a motor. Yet anotherobject of the present invention is to provide a drive control method ofthe motor superior in operation efficiency. Still another object of thepresent invention is to provide various power drivers employing such amotor.

In order to achieve the foregoing objects, the present inventionprovides a motor having a combination of a plurality of coil pairs and apermanent magnet, wherein these coil pairs are supplied with anexcitation signal from a drive circuit so as to be excited at alternateopposite poles, and the permanent magnet is constituted such that theplurality of polar elements is disposed to become alternating oppositepoles; the drive circuit is constituted to supply an excitation signalhaving a prescribed frequency to the coil pairs, and relatively move thecoil pairs and permanent magnet with the magnetic attraction—repulsionbetween the coils and permanent magnet; and the drive circuit isconstituted to supply to the coil pairs a waveform signal correspondingto the pattern of the back electromotive voltage to be generated inaccordance with the relative movement between the coil pairs andpermanent magnet.

In an embodiment of the present invention, the drive circuit comprises ahall element sensor for detecting the magnetic variation of thepermanent magnet, this hall element sensor is used for outputting awaveform; for example, a sinusoidal waveform or a triangular waveform,corresponding to the magnetic change, and the drive circuit isconstituted to directly supply the output of this hall sensor to thecoil pairs. The motor further comprising a plurality of phases as thecoil pairs, and a hall element sensor is disposed for each phase. Thedisposition of coils between the coil pairs of the plurality of phasesis mutually shifted, and the disposition of the hall element sensorbetween the plurality of phases is also shifted. The shift amount of thecoil position of the coil pairs of the plurality of phases is determinedso as to enable the rotation of the permanent magnet when the outputfrom the hall element is supplied to the coil pairs of the plurality ofphases upon supplying power to the drive circuit. A rotor formed fromthe permanent magnet is disposed between the plurality of coil phasesarranged circularly. The drive circuit supplies a rectangular wave toeach of the phase coils when the motor is started, and the drive circuitsupplies the back electromotive voltage waveform to each of the phasecoils while the motor is in a state of operational stability.

Further, the present invention also provides a drive system of an ACmotor, wherein the AC motor excites the electromagnetic coil with awaveform that is identical to the back electromotive force waveforminherent in the AC motor. Preferably, the waveform is formed with a hallelement sensor. More preferably, the waveform formed with the hallelement sensor is formed via PWM control means.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram showing the frame format and principal of operationof the magnetic structure pertaining to the present invention;

FIG. 2 is a diagram showing the principal of operation subsequent toFIG. 1;

FIG. 3(1) is an equivalent circuit diagram of coil pairs in which aplurality of coils is connected serially; and FIG. 3(2) is an equivalentcircuit diagram in a case of such coils being connected in parallel;

FIG. 4 is a block diagram of the drive circuit for supplying anexcitation signal to a coil pair;

FIG. 5 is an exploded perspective view of the motor;

FIG. 6 is a characteristic diagram showing a case of supplying arectangular wave to the coil for explaining the principal of the presentinvention;

FIG. 7 is a principal diagram showing a situation where backelectromotive force is generated in the coil;

FIG. 8 is a characteristic diagram showing a case where a waveform thatis roughly equivalent to a sinusoidal waveform of the back electromotiveforce is supplied to the coil as the drive waveform for explaining theprincipal of the present invention;

FIG. 9 is a block diagram of the drive circuit for supplying asinusoidal waveform from the hall element sensor to the coil;

FIG. 10 is a waveform diagram respectively showing the state of waveformcontrol in the drive circuit illustrated in FIG. 9;

FIG. 11 is a drive circuit block diagram which enables the hysteresiscontrol in the drive circuit;

FIG. 12 is a waveform diagram respectively showing the state of thewaveform control thereof;

FIG. 13 is a functional block diagram of the drive circuit showing astate where the detection waveform of the respective phase coils isdirectly supplied to the PWM conversion control unit;

FIG. 14 is a waveform diagram showing the PWM control operation;

FIG. 15 is a plan view of the rotor for showing another example of thepermanent magnet (rotor); and

FIG. 16 is a waveform diagram of the triangular waveform outputgenerating in the respective phase sensors upon using the rotor as themotor.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 and FIG. 2 are diagrams showing the principal of operation of themotor pertaining to the present invention. This motor has a constitutionwhere a third permanent magnet 14 is interposed between a first coilpair (A phase coil) 10 and a second coil pair (B phase coil) 12. Thecoils and permanent magnet may be constituted circularly (arc, circle)or linearly. When formed circularly, either the permanent magnet or thecoil phase functions as the rotor, and, when formed linearly, one of theabove becomes a slider.

A first coil pair 10 comprises a constitution in which the coils 16alternately excitable to the opposite poles are sequentially aligned ina prescribed spacing, preferably an even spacing. FIG. 5 is anequivalent circuit diagram of this first coil pair. According to FIG. 1and FIG. 2, as described later, with a two-phase excitation coil, allcoils are excited to be constantly driven against the two-phase excitingcoil during the start-up rotation (2π) with the foregoing polarity.Therefore, a drive means such as a rotor or slider can be rotated anddriven at high torque.

As shown in FIG. 3(1), a plurality of electromagnetic coils 16 (magneticunit) to be alternately excited at opposite poles is connected seriallyin even spacing. Reference numeral 18A is a block showing the drivecircuit for applying a frequency pulse signal to these magnetic coils.When an excitation signal for exciting the coils is sent from theexcitation circuit to the electromagnetic coils 16, the respective coilsare pre-set to be excited such that the direction of the magnetic poleswill alternate between the adjacent coils. As shown in FIG. 3(2), theelectromagnetic coils 16 may also be connected in parallel. Thestructure of these coils are the same for both A and B phase coils.

When a signal having a frequency for alternately switching, inprescribed cycles, the direction of the polarity of the suppliedexcitation current is applied from the excitation circuit 18A to theelectromagnetic coils 16, as shown in FIG. 1 and FIG. 2, a magneticpattern which alternately changes the polarity on the side facing therotor 14 from N pole→S pole→N pole is formed in the A phase coil pair10. When the frequency signal becomes a reverse polarity, a magneticpattern is generated for alternately changing the polarity, which is onthe third magnetic body side, of the first magnetic body from S pole→Npole→S pole. As a result, the excitation pattern appearing in the Aphase coil pair 10 will periodically change.

Although the structure of the B phase coil pair is the same as the Aphase coil pair, the electromagnetic coils 18 of the B phase coil pairdiffers with respect to the point that it is aligned by beingpositionally shifted in relation to the [electromagnetic coils] 16 ofthe A phase coil pair. In other words, the array pitch of the coil inthe A phase coil pair and the array pitch of the B phase coil pair aredisposed in an offset so as to have a prescribed pitch difference(angular difference). This pitch difference is preferably the (singlerotation) of the angle in which the permanent magnet 14 movescorresponding to 1 cycle (2π) of the excitation current frequency inrelation to the coils 16, 18; for instance π/6 (π/(2/M): M is the numberof sets of permanent magnet (N+S) where M=3).

The permanent magnet is now explained. As depicted in FIG. 1 and FIG. 2,the rotor 14 formed from a permanent magnet is disposed between atwo-phase coil pair, and a plurality of permanent magnets 20 (marked outin black) having alternately reverse polarities is aligned in a line(linearly or in an arc) in prescribed spacing, preferably in evenspacing. An arc shape includes loops such as a perfect circle or an ovalshape, as well as indefinite circular structures, half circles, fanshapes, and so on.

The A phase coil pair 10 and B phase coil pair 12 are disposed via equalspacing, and a third magnetic body 14 is disposed between the A phasecoil pair and B phase coil pair. The array pitch of the permanent magnet20 is roughly the same as the array pitch of the magnetic coil in the Aphase coil 10 and B phase coil 12.

Next, the operation of the magnetic structure in which the foregoingthird magnetic body is disposed between the first magnetic body 10 andsecond magnetic body 12 is explained with reference to FIG. 1 and FIG.2. Let it be assumed that, based on the foregoing excitation circuit(reference numeral 18 illustrated in FIG. 3; to be described in detaillater), the excitation pattern shown in FIG. 1(1) is being generated ata certain moment in the electromagnetic coils 16, 18 of the A phase coiland B phase coil. Here, a magnetic pole in the pattern of→S→N→S→N→S→isgenerated in the respective coils 16 on the surface facing the side ofthe permanent magnet 14 of the A phase coil 10, and a magnetic pole inthe pattern of→N→S→N→S→N→is generated in the coil 18 on the surfacefacing the side of the permanent magnet 14 of the B phase coil 12. Inthe diagrams, the magnetic relation between the permanent magnet and therespective phase coils is illustrated, and a repulsive force will arisebetween the same poles and an attractive force will arise betweenopposite poles.

The next instant, as shown in FIG. 1(2), when the polarity of the pulsewave applied to the A phase coil via the drive circuit 18 is reversed, arepulsive force will arise between the magnetic pole generated to thecoils 16 of the A phase coil 10 and the magnetic pole of the permanentmagnet 20. Meanwhile, since an attracting force is generated between themagnetic pole generated to the coils 18 of the B phase coil 12 and themagnetic pole on the surface of the permanent magnet, as shown in FIG.1(1) to FIG. 2(5), the permanent magnet 14 will sequentially moverightward in the diagram.

A pulse wave having a phase lag in comparison to the exciting current ofthe A phase coil applied to the coils 18 of the B phase coil 12, and, asshown in FIG. 2(6) to (8), the magnetic pole of the coils 18 of the Bphase coil 12 and the magnetic pole on the surface of the permanentmagnets 20 repel against each other, and move the permanent magnet 14further rightward. FIG. 1(1) to FIG. 2(8) illustrate a case where therotor 14 engages in a rotation corresponding to π, and FIG. 3(9) onwardillustrate a case where such rotor 14 engages in a rotationcorresponding to π→2π. As described above, the rotor will rotate bysupplying a drive current (voltage) signal of a prescribed frequencywith a shifted phase to the A phase coil array and B phase coil array.

When the A phase coil array, B phase coil array and the permanent magnetare formed in an arc, the magnetic structure depicted in FIG. 1 willbecome a structure of a rotating motor, and, when these are formedlinearly, the magnetic structure thereof will become a linear motor.Excluding the portions of the permanent magnet such as a case or rotorand the electromagnetic coil can be reduced in weight by employing anon-magnetic body such as resin (including carbon) or ceramics, and arotating power drive superior in a power-weight ratio can be realizedwithout generating iron loss as a result of opening the magnetic circuitwithout using a yoke.

According to this magnetic structure, since the permanent magnet is ableto move upon being subject to the magnetic force from the A phase coiland the B phase coil, the torque upon moving the permanent magnet willincrease, and, since the torque/weight balance will become superior, asmall motor capable of driving at a high torque can be provided thereby.

FIG. 4 is a block diagram showing an example of an excitation circuit18A for applying an exciting current to the electromagnetic coils 16 ofthe first magnetic body of the A phase coil array and theelectromagnetic coils 18 of the B phase coil array. This excitationcircuit is structured to respectively supply controlled pulse frequencysignals to the A-phase electromagnetic coils 16 and the B-phaseelectromagnetic coils 18. Reference numeral 30 is a quartz oscillator,and reference numeral 31 is an M-PLL circuit for generating a referencepulse signal by M-dividing this oscillation frequency signal.

Reference numeral 34 is a sensor (i.e., a hall element sensor fordetecting the magnetic field change of the permanent magnet as describedlater) for generating a position detection signal corresponding to therotational speed of the rotor 14 formed from the permanent magnet.Reference numeral 34A is an A phase side sensor for supplying adetection signal to the driver circuit of the A phase electromagneticcoil, and reference numeral 34B is a B phase side sensor for supplying adetection signal to the driver circuit of the B-phase electromagneticcoil.

The detection signals from these sensors 34A, 34B are respectivelyoutput to the driver 32 for supplying an exciting current to therespective phase coil arrays. Reference numeral 33 is a CPU and outputsa prescribed control signal to the M-PLL circuit 31 and the driver 32.The driver 32 is constituted to supply the detection signal from thesensor directly, or via PWM control, to the electromagnetic coil.Reference numeral 31A is a control unit for supplying a PWM controlreference wave to the driver. Although the magnetic sensor 34A for the Aphase coil array and the magnetic sensor 34B for the B phase coil arrayare respectively detecting the magnetic field of the permanent magnet byestablishing a phase difference, the detection signal isphase-controlled as necessary and supplied to the driver 32. Referencenumeral 35 is a

sensor phase control unit.

FIG. 5 is a perspective view of the motor, wherein FIG. 5(1) is aperspective view of the motor; FIG. 5(2) is a schematic plan view of therotor; FIG. 5(3) is a side view thereof; FIG. 5(4) is a diagram showingan A phase electromagnetic coil array; and FIG. 5(5) is a diagramshowing a B phase electromagnetic coil array. The reference numeralsused in FIG. 5 are the same as the structural components correspondingto the foregoing diagrams.

The motor comprises a pair of A phase coil array 10 and B phase coilarray 12 corresponding to a stator, as well as the permanent magnet 14constituting the rotor described above, and the rotor 14 is rotatablydisposed around the axis 37 and between the A phase coil array and Bphase magnetic body. The rotating axis 37 is fitted into an opening inthe center of the rotor such that the rotor and rotating axis can rotateintegrally. As shown in FIG. 5(2), (4) and (5), six permanent magnetsare provided to the rotor in even spacing around the circumferentialdirection thereof, polarities of the permanent magnets are made to bemutually opposite, and six electromagnetic coils are provided to thestator in even spacing around the circumferential direction thereof.

The A phase sensor 34A and B phase sensor 34B are provided to the innerside wall of the case of the A phase coil array via a phase shift(distance corresponding to π/6). The A phase sensor 34A and B phasesensor 34B are subject to mutual phase shifts for providing a prescribedphase different to the frequency signal to be supplied to the A phasecoil 16 and the frequency signal to be supplied to the B phase coil 18.

As the sensor, it is preferable to use a hall element employing the halleffect and which is capable of detecting the position of the permanentmagnet from the change in the magnetic pole pursuant to the movement ofthe permanent magnet. As a result of employing this sensor, when the Spole of the permanent magnet to the subsequent S pole is set to 2π, thehall element will be able to detect the position of the permanent magnetregardless of where the permanent magnet is located.

The principal of the present invention is now explained.

FIG. 6(1) is a diagram showing the potential change at both ends of thecoil when a rectangular wave is supplied to the coil. FIG. 6(2) is adiagram showing the back electromotive voltage waveform of both ends ofthe coil. FIG. 6(3) is a diagram showing the current consumptionwaveform of both ends of the coil. FIG. 7 is a principal diagram forexplaining the back electromotive force that is generated in the coilwhen the permanent magnet disposed between two-phase coil arrays movesrightward in the diagram.

The back electromotive voltage (V) is defined with Bh*CI*P, Bh[T] is thehorizontal magnetic flux density (center of coil), CL(m) is the coillength, and P[m/s] represents the movement speed of the coil. Asinusoidal back electromotive voltage waveform represented with 8-1 isgenerated in the A phase coil 16, and a sinusoidal back electromotivevoltage waveform represented with 8-2 having a phase difference based onthe alignment of the A phase coil array and the alignment of the B phasecoil array is generated in the B phase coil 18.

The double-ended voltage in the π area of FIG. 6(3) will have anincreased current since the potential difference is significant due tothe difference between the applied voltage and the back electromotiveforce. Thus, although the generated torque of the motor will increase,the efficiency of the motor will deteriorate. Efficiency (η) is definedby:η=(mechanical output/input voltage)*100(%).

Meanwhile, FIG. 8(1) is a diagram showing the voltage waveform of bothends of the coil when a sinusoidal signal (supplied voltage waveform)that is identical to the back electromotive force waveform is applied toboth ends of the coil. FIG. 8(2) is a diagram showing the voltageconsumption waveform of the coil. Only the waveform distortion isgenerated in the voltage at both ends of the coil shown in area π ofFIG. 8(2) based on the difference between the supplied voltage waveformand the back electromotive voltage waveform, and the current consumptionwaveform of both ends of the coil will become an extremely small currentvalue as evident from the vertical axis scale of FIG. 6(2) and thevertical axis scale of FIG. 8(2). Thus, the efficiency can beconsiderably improved. By improving the waveform distortion, theefficiency can be further improved. The analog output-type hall elementis able to output a waveform corresponding to the back electromotivevoltage waveform. As a result of exciting the coil with a waveform thatis the same as the back electromotive force waveform, the efficiencywill improve two-fold or three-fold in comparison to exciting the coilwith a rectangular wave. Therefore, when this motor is employed in theload, the simultaneous pursuit of the drive characteristics andefficiency motor can be sought by supplying a rectangular waveform tothe coil in a situation of emphasizing the start-up torque upon startingor accelerating the operation of the load, and supplying a sinusoidalwave to the coil during a stable drive.

FIG. 9 is a block diagram of the drive circuit for directly driving thedriver with an analog sensor (hall element sensor). In other words, thissensor, as shown in FIG. 10(1) described later, generates a sinusoidaloutput wave that is closest to the back electromotive force waveform, asa result of supplying the output from this sensor directly to the coil,the motor can be driven at the maximum efficiency. Reference numeral 100is an amplifier of the sensor output. Reference numeral 101 is thenormal/reverse rotation control circuit of the rotor. The rotation ofthe rotor can be controlled by coercively reversing the polarity of thedetection waveform from the sensor to be supplied to the coil of the Aphase or B phase. Reference numeral 93 is the formation unit of acommand signal to be supplied to this control circuit. The detectionsignal from the A phase sensor 34A is amplified and supplied to the Aphase coil. The detection signal from the B phase sensor 34B isamplified and supplied to the B phase coil.

FIG. 10 is a diagram showing a state of controlling the waveform in thedrive circuit, and FIG. 10(1) shows the analog output waveform(sinusoidal waveform) from the A phase sensor. FIG. 10(2) is the outputwaveform from the B phase sensor. As described above, since the twosensors are disposed with a phase difference, the phase is shifted. FIG.10(3) is the A1 phase drive waveform (voltage waveform in theorientation of terminal A1→A2 illustrated in FIG. 3) to be supplied tothe A phase coil, and FIG. 10(4) is the A2 phase drive waveform (voltagewaveform in the orientation of terminal A2→A1 illustrated in FIG. 3) tobe supplied to the A phase coil. FIG. 10(5) is the B1 phase drivewaveform to be supplied to the B phase coil, and FIG. 10(6) is the B2phase drive waveform. FIG. 10(7) is the waveform of both ends (betweenA1 and A2) between the A phase coil pair, and FIG. 10(8) is the waveformof both ends (between B1 and B2) between the B phase coil pair. Thesinusoidal output waveform of the sensor is supplied to the coil pair ofthe respective phases.

FIG. 11 is a block diagram of the drive circuit for converting theanalog output from the sensor into a rectangular wave and supplying thisto the coil pair. As described above, when it is necessary to operatethe motor at a high torque, there is significance in supplying therectangular wave to the coil. The rotation speed of the motor isdetected with the rotation speed sensor not shown, and, when therotation speed of the motor exceeds a prescribed value (during a stabledrive), the drive circuit directly supplies, in place of the rectangularwave, the analog output of the sensor to the coil array.

In FIG. 11, reference numeral 121 is the variable volume for controllingthe hysteresis control, and reference numeral 120 is a windowcomparator, and reference numeral 122 is a multiplexer. The output valueof the respective phase sensors is supplied to the window comparator, anH level signal and L level signal are formed upon comparing the upperand lower values of the sensor output and hysteresis level, and this isoutput as the A1 phase drive signal or A2 phase drive signal pursuant tothe switching control of the multiplexer. The drive of the B1 phase coiland B2 phase coil is the same. Reference numeral 123 is the rotationaldirection control unit of the normal rotation or reverse rotation of therotor.

FIG. 12 is a waveform diagram based on the control circuit of FIG. 12,and FIG. 12(1) is a sinusoidal output waveform of the A phase sensor,and FIG. 12(2) is the output waveform of the B phase sensor. FIG. 12(3)is a rectangular waveform of the frequency to be supplied to the A phasecoil pair as the A1 phase drive signal, and FIG. 12(4) is a rectangularwaveform to be supplied to the A phase coil pair as the A2 phase drivesignal. FIG. 12(5) and FIG. 12(6) are rectangular waveforms to besupplied to the B phase coil pair. FIG. 12(7) is a voltage waveform ofboth ends of the A phase coil pair, and FIG. 12(8) is the voltagewaveform of both ends of the B phase coil pair. In FIG. 12, thehysteresis adjustment volume may be controlled from the likes of anexternal CPU in a D/A converter. As a result of making the hysteresislevel variable, the duty of the rectangular wave is changed, and thetorque control of the motor characteristics is enabled. For example,upon starting the motor, the hysteresis level is set to minimum, and themotor is driven giving preference to the torque and sacrificing theefficiency. Further, when the motor is in a state of operationalstability, the hysteresis level is set to maximum to drive the motorgiving preference to high efficiency.

FIG. 13 is a block diagram of the drive circuit showing that the outputof the sensor is supplied to the PMW converter 140, the analog outputvalue of the sensor is compared with the reference wave not shown, andthe duty ratio of the rectangular wave to be supplied to the respectivecoils is controlled (PWM controlled). In other words, as illustrated inFIG. 14, the output of the respective phase sensors (1) and (2) isduty-controlled, and becomes the voltage at both ends to be supplied tothe respective phase coil pairs as shown in FIG. 14(3) and FIG. 14(4).

FIG. 15 is a diagram showing a plan view of the permanent magnet (rotor)14 in which a plurality of permanent polar elements 150 has beenintegrated. Whereas the space between the respective permanent polarelements of the rotor is formed from a non-magnetic body in FIG. 1 andFIG. 2, with the rotor in this embodiment, the permanent polar elementsare closely adhered to each other without going through an area betweenthe respective permanent polar elements 150. Reference numeral 152 isthe rotating axis of the rotor, and reference numeral 154 is therotator. A plurality of permanent polar elements is continuously alignedaround the peripheral edge of this rotator. With the [rotor] illustratedIn FIG. 15, a triangular waveform back electromotive force is generatedas shown in FIG. 16. Therefore, the motor can be operated at maximumefficiency by forming the detection signal of the respective phase coilarray sensors into a triangular wave and supplying this to therespective phase coils.

Accordingly, even with electric motors of other methods, the motoritself can be driven at a high efficiency by exciting the coil of themotor with a waveform that is the same as the waveform of the backelectromotive force generated from the electric motor, where theefficiency (work/power ratio) is not inherent in the electric motor. Inother words, according to the present invention, a highly efficientmotor, drive system and drive method can be realized.

1. A drive circuit for an AC motor, the AC motor comprising acombination of a coil body and a permanent magnet, and a pair of Hallelement sensors, the coil body having a plurality of coils, thepermanent magnet having a plurality of magnet pole elements, theplurality of magnet pole elements being arranged to become alternatingopposite poles to rotate relative to the coil body, and each of the Hallelement sensors being positioned at a different location and provided todetect magnetic alternation in accordance with a relative movementbetween the coil body and the permanent magnet and to output an analogsignal corresponding to a waveform having a pattern of a backelectromotive force voltage generated in the coil body, the drivecircuit comprising: a first unit constituted to output a referencelevel; a second unit constituted to compare the analog signal output bythe Hall element sensors with the reference level output by the firstunit; and a third unit constituted to generate and output a drive signalto the coil body by switching a voltage based on results of a comparisonby the second unit, wherein the first unit outputs an upper level and alower level as the reference level, wherein the second unit compares theanalog signal with both the upper level and the lower level, and whereinthe third unit generates a pair of the drive signals, each drive signalrespectively corresponding to results of the comparison for either theupper level or the lower level.
 2. The drive circuit according to claim1, further comprising a fourth unit constituted to alter the referencelevel relative to the analog signal.
 3. The drive circuit according toclaim 1 or 2, further comprising a fifth unit constituted to change adirection of rotation of the AC motor by reversing the polarity of thevoltage switched by the third unit.
 4. The drive circuit according toclaim 1, wherein the third unit is a multiplexer.
 5. The drive circuitaccording to claim 1, wherein the third unit provides the drive signalthat is a rectangular waveform until a rotation speed of the AC motorexceeds a prescribed value.
 6. The drive circuit according to claim 1,further comprising a sixth unit constituted to provide a waveformcorresponding to the analog signal when a rotation speed of the AC motorexceeds a prescribed value.